With the development of faster and more powerful processors in many electronic devices power consumption has become an issue of increasing importance, in particular with regard to mobile electronic devices with limited power sources. Mobile devices such as, but not limited to, mobile telephones, personal data appliances, personal digital assistants (PDAs), lap top computers and the like, are sometimes required to operate for long periods of time before their power source can be recharged.
Accordingly, such portable devices implement some form of power management scheme where functional components of the device, such as processors, memories, interfaces, radios, physical layers (PHYs), power regulators, crystal oscillators etc of the device can be placed in two or more different power modes.
A power management unit sequencer block, sometimes referred to as a PSEQ (Power SEQuencer) can be used to control the enabling of different power modes of one or more components of an electronic device. Such a unit needs to handle a number of different inputs and outputs. For example, a typical PSEQ may include:                2 power ON inputs to capture a user power-up command;        an external regulator enable (REG_EN) output to trigger the power-up of any power regulator present in the electronic device.        a <<configuration>> (CONFIG) input used in general to set the voltage of a power regulator.        a test mode enable (TM_EN) input to engage a PSEQ test mode used for production testing.        A test mode serial digital interface to give PSEQ access to the production test machine when test mode is enabled. Such a serial interface has in general 3 inputs (serial in, capture) and 1 output (serial out). The serial CLK is provided by indirect means since it can be shared with other cells in the chip.        
In some designs of PMU sequencer blocks, each node of the PSEQ is mapped to a specific function.
Other functional block components of integrated circuits and the like are also provided with a limited number of nodes. Usually each node of such components are mapped to a specific input or output function.
In some cases multiplexing of input and or output signals can be used. Analogue comparators may also be implemented to increase multiplexing capability. Such approaches require specific number of nodes to cover the I/O functions. The use of analogue cells may also lead to an increase in current consumption.